A common type of conveyor for moving containers in a processing environment has a rotating screw on one side of a linear series of containers and a wall or bar guide on the other side of the line of containers. The containers are held in the helical groove of the screw by the guide wall and moved along by the rotation of the screw. The conveyor positions the containers in a process station, for example a filling machine that fills each container with the required material. Accurate and efficient filling is predicated on alignment between the filling station and the series of containers that are conveyed along a central line of travel. When a different size container is to be processed, the spacing between the screw and the guide wall must be adjusted. Since the screw is connected to a driving mechanism for rotation, space adjustment is generally made by changing the position of the guide wall. Moving the guide wall relative to the screw will define a new central line of travel for the containers. The filling machine then must be moved to be in alignment with the new line of travel along which the different size containers are to be conveyed. This step of aligning the filling machine with the line of travel of the containers is time consuming and may result in loss of accuracy of filling. Therefore, a need exists for an apparatus that retains a constant line of container travel regardless of the size of the containers being processed, thus reducing changeover time and increasing filling efficiency and accuracy.